Annalee Newitz

"The human sense of smell is far better at guiding us through our everyday lives than we give it credit for," said cognitive neuroscientist Johan Lundström. He was referring to what he and a research team just discovered, which is that humans can actually tell how much fat is in their food just by smelling it.

"That we have the ability to detect and discriminate minute differences in the fat content of our food suggests that this ability must have had considerable evolutionary importance," continued Lundström in a statement from the Monell Chemical Senses Center where he works. Our appetite for fatty food probably evolved over thousands of years, as a good incentive for us to guzzle tons of easily-stored calories. We already knew that people could taste the difference between fatty and non-fatty, which many of us sense as the difference between "holy crap delicious" and "that's okay."

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What Lundström and his colleagues wanted to know, however, was whether humans had evolved other ways to recognize high calorie foods. So they conducted a series of tests, where people in the U.S. and the Netherlands were asked to determine the fat content of milk by smell. The published their findings in PLoS One today.

Write the researchers:

Over all three experiments, results clearly demonstrated that humans were able to detect minute differences between milk samples with varying grades of fat, even when embedded within a milk odor. Moreover, we found no relation between this performance and either BMI or dairy consumption, thereby suggesting that this is not a learned ability or dependent on nutritional traits. We argue that our findings that humans can detect the fat content of food via odors may open up new and innovative future paths towards a general reduction in our fat intake, and future studies should focus on determining the components in milk responsible for this effect.

One possible reason why people could be sensitive to the smell of fat in milk could be that they were voracious consumers of dairy and thus conditioned to sense it. But the researchers found no difference between the fat-sensing abilities of people with different eating habits and different body mass indexes (the body mass index, or BMI, measures how much of your body weight is fat).

It appears that humans really do have a sense we never realized we had. If you smell two dishes, you'll be able to tell which one is fattier. The researchers hope this can help in future studies of how people can learn to regulate their diets to include less fat.